Vesper sparrow (Pooecetes gramineus affinis) COSEWIC assessment and status report: chapter 2

Executive Summary

Vesper Sparrow affinis subspecies

Pooecetes gramineus affinis

Species information

Three subspecies of Vesper Sparrows breed in Canada. The Vesper Sparrow affinis subspecies, Pooecetes gramineus affinis, is the rarest subspecies, with a disjunct population and a restricted range. The other recognized subspecies have much larger, stable populations. The Vesper Sparrow is a relatively large sparrow with distinctive chestnut wing coverts, white outer tail feathers and a white eye ring.

Distribution

The Vesper Sparrow affinis subspecies, also called Coastal Vesper Sparrow, occurs west of the Cascade mountain range in southwestern British Columbia, western Washington, Oregon, and northwestern California. In British Columbia, its historic distribution was restricted to the lower Fraser River valley and southeastern Vancouver Island. There is currently only one known site where it continues to breed in British Columbia. Based on proximity to the affinis population in Washington State, it is accepted by most authorities that Vesper Sparrows breeding in the Georgia Depression region of southwestern British Columbia are a continuation of that population. Vesper Sparrow breeding season records in the Georgia Depression date from 1890.

Habitat

The Vesper Sparrow breeds in sparsely vegetated, grassland habitats with scattered trees or shrubs. Structural diversity is important because these sparrows use the taller perches for singing whereas open areas are used for foraging.

Biology

Vesper Sparrows nest on the ground. The breeding season of Coastal Vesper Sparrows in British Columbia is approximately late April to mid-July. Breeding site fidelity is likely strong. During the breeding season, the diet consists primarily of insects, although seeds are also taken. Vesper Sparrows can adapt to modified habitats. However, there is potentially a greater risk of nest failure as these areas are often mowed or have other human induced disturbance issues.

Population sizes and trends

The Canadian breeding population of the Coastal Vesper Sparrow is currently estimated at five to ten breeding pairs. Although historic population estimates are not available, the population has probably declined based on the fact that fewer localities are now occupied. Populations have also declined in Washington and Oregon.

Limiting factors and threats

Loss or alteration of habitat is the primary threat to Vesper Sparrows throughout the species’ range. Modern agricultural practices and urban development have both contributed to habitat alteration. Vesper Sparrow habitat is currently very scarce on south eastern Vancouver Island and in the lower mainland. Other threats include predation by domestic and feral cats, a predator that occurs in higher densities in urbanized areas. Due to population declines in adjacent Washington State, it is increasingly unlikely that there will be a source of dispersing birds from that jurisdiction, to augment the existing population on Vancouver Island.

Special significance of the species

The distribution of the Coastal Vesper Sparrow is disjunct from populations of other subspecies and therefore has a genetic diversity that is important to conserve. The Coastal Vesper Sparrow is considered a priority species for recovery efforts by the Garry Oak Ecosystems Recovery Team, Vertebrates at Risk Recovery Implementation Group. Improvements to the habitat that benefit this species will also likely benefit other, lesser known species in this rare ecosystem.

Existing protection or other status designations

The Coastal Vesper Sparrow is on the Red List in British Columbia. It is a candidate for the endangered species list In Washington and in Oregon is considered a ‘state sensitive species’.

COSEWIC History

The Committee on the Status of Endangered Wildlife in Canada (COSEWIC) was created in 1977 as a result of a recommendation at the Federal-Provincial Wildlife Conference held in 1976. It arose from the need for a single, official, scientifically sound, national listing of wildlife species at risk. In 1978, COSEWIC designated its first species and produced its first list of Canadian species at risk. Species designated at meetings of the full committee are added to the list. On June 5th 2003, the Species at Risk Act(SARA) was proclaimed. SARA establishes COSEWIC as an advisory body ensuring that species will continue to be assessed under a rigorous and independent scientific process.

COSEWIC Mandate

The Committee on the Status of Endangered Wildlife in Canada (COSEWIC) assesses the national status of wild species, subspecies, varieties, or other designatable units that are considered to be at risk in Canada. Designations are made on native species for the following taxonomic groups: mammals, birds, reptiles, amphibians, fishes, arthropods, molluscs, vascular plants, mosses, and lichens.

COSEWIC Membership

COSEWIC comprises members from each provincial and territorial government wildlife agency, four federal entities (Canadian Wildlife Service, Parks Canada Agency, Department of Fisheries and Oceans, and the Federal Biodiversity Information Partnership, chaired by the Canadian Museum of Nature), three non-government science members and the co-chairs of the species specialist subcommittees and the Aboriginal Traditional Knowledge subcommittee. The Committee meets to consider status reports on candidate species. 

Definitions (2006)

Species
Any indigenous species, subspecies, variety, or geographically defined population of wild fauna and flora.

Extinct (X)
A species that no longer exists.

Extirpated (XT)
A species no longer existing in the wild in Canada, but occurring elsewhere..

Endangered (E)
A species facing imminent extirpation or extinction..

Threatened (T)
A species likely to become endangered if limiting factors are not reversed..

Special Concern (SC)*
A species of special concern because of characteristics that make it particularly sensitive to human activities or natural events.

Not at Risk (NAR)*
A species that has been evaluated and found to be not at risk..

Data Deficient (DD)***
A species for which there is insufficient scientific information to support status designation.

* Formerly described as “Vulnerable” from 1990 to 1999, or “Rare” prior to 1990.
** Formerly described as “Not In Any Category”, or “No Designation Required.”
*** Formerly described as “Indeterminate” from 1994 to 1999 or “ISIBD” (insufficient scientific information on which to base a designation) prior to 1994.

The Committee on the Status of Endangered Wildlife in Canada (COSEWIC) was created in 1977 as a result of a recommendation at the Federal-Provincial Wildlife Conference held in 1976. It arose from the need for a single, official, scientifically sound, national listing of wildlife species at risk. In 1978, COSEWIC designated its first species and produced its first list of Canadian species at risk. Species designated at meetings of the full committee are added to the list.

The Canadian Wildlife Service, Environment Canada, provides full administrative and financial support to the COSEWIC Secretariat.

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